1. Field
This application relates generally to computer graphics, and more specifically to computer systems and processes for the animation of feathers.
2. Related Art
Media productions have employed increasingly complex animations in order to construct increasingly realistic images. In addition to animating surfaces, increasing attention has been directed towards skin-attached elements, such as feathers, hair, and fur.
Animating feathers, in particular, has been a challenging subject since the early days of animation. Birds of early animation films were often secondary characters with relatively few, unrealistic feathers. Although more life-like effects have been achieved in modern animation, challenges remain, especially for animating birds with a large number of feathers throughout an animation sequence. For example, when using conventional animation techniques, individual feathers are likely to intersect with one another or with the skin surface such that the animation appears unrealistic. In addition to these intersections (also known as interpenetrations or collisions), the layering of the feathers may be inconsistent when the frames are independently developed for an animation sequence, causing feathers to “pop” from frame to frame.
A number of solutions have been tried. For example, one method sets the feathers at fixed angles with sufficient spacing between feathers to avoid interpenetrations, but the result may appear unnatural. Another approach calculates reference offsets for every control point of a feather and maintains these offsets throughout the animation sequence. While this method makes interpenetrations less likely, it does not eliminate them. One common approach is to process a bird's feathers from tail to head, deforming each feather such that it does not intersect previously positioned feathers. This approach does solve the interpenetration problem, but is susceptible to frame coherency problems (popping) and volume inflation problems (puffing). By making the coloring of the feathers uniform, a certain degree of feather interpenetration can be made tolerable (i.e., minimally visible), at the expense of constraining artistic expression for the animated character. None of these techniques produce particularly realistic animated sequences of feathers, and furthermore, manual intervention may have to be introduced to correct for the defects of an automated approach to animation.
Thus, there is a need for improved animation of feathers and related skin-attached elements.